System and method for preventing blow-by of liquefied gases

ABSTRACT

A system and method for preventing blow-by of liquefied gases is disclosed, which senses the occurrence of blow-by and shuts off the source of the liquefied gas. As one example, a system for preventing blow-by of LN2 is disclosed, which includes a temperature sensor located near an exhaust line of a heat exchanger, a shutoff valve located in an inlet line, and a controller coupled to the temperature sensor and the shutoff valve. The sensor measures the temperature of the exhaust, and provides a signal to the controller that indicates if the temperature of the exhaust approaches the temperature of LN2. If the exhaust temperature approaches the temperature of LN2, the controller sends a signal to the shutoff valve, which causes the valve to close and stops the flow of LN2 to the heat exchanger involved. The controller can also send an alarm signal to a display, which indicates to a user that the blow-by is occurring. If the exhaust temperature increases significantly above the temperature of LN2 (e.g., blow-by is no longer occurring), the controller can send a second signal to the shutoff valve, which causes the valve to open and resume the flow of LN2.

FIELD OF THE INVENTION

The present invention relates generally to the process control field, and more specifically, but not exclusively, to a system and method for preventing blow-by of liquefied gases.

BACKGROUND OF THE INVENTION

Liquefied gases, such as liquid nitrogen (LN2), liquid helium or liquid oxygen, are used in a wide range of cryogenic (extremely cold) applications. For example, LN2 is often used as a coolant for sensitive electronic sensors, low noise amplifiers, semiconductor product testing, and other industrial applications. Also, LN2 is used for cryogenics research, preserving biological materials, freezing food products, and heat transfer applications that require the extremely low temperatures involved.

A significant problem that arises with the use of liquefied gases is commonly referred to as “blow-by”. For example, when LN2 is transferred from one containment vessel to another (e.g., storage tank to a Dewar), a vent is provided in the receiving vessel to bleed off excess nitrogen gas and allow additional LN2 to enter the vessel. The excess nitrogen gas is typically vented to the surrounding environment. However, if the Dewar or other receiving vessel is filled to capacity, excess LN2 (rather than nitrogen gas) begins to blow-by or exit through the vent. In less serious cases, the vented LN2 can rain down as super-cooled droplets that “burn” personnel and damage equipment. In the more severe cases of blow-by (e.g., while filling a Dewar), large amounts of LN2 can be released to the surrounding environment in an uncontrolled fashion and produce a large, dangerous cloud of boiling white LN2 “smoke”. Such large amounts of vented LN2 can result in serious bodily injuries such as bums and asphyxiation, severe damage to equipment, and can require a full-blown response by local authorities along with their hazardous materials cleanup teams. Also, liquefied gases such as LN2 are relatively expensive to procure, and the economic cost due to blow-by is a significant expense to have to incur.

Liquefied gases are also used for heat transfer applications. For example, LN2 is used as a super-cooled refrigerant for certain heat exchangers. Typically, the LN2 is piped into a heat exchanger through an inlet tube, changed to nitrogen gas during the heat exchange process, and the excess gaseous nitrogen is output from the heat exchanger through an exhaust tube. The exhaust tube is often constructed to vent the excess gaseous nitrogen to the outside air. However, if the heat exchanger is overwhelmed with the incoming LN2 (e.g., the heat exchange rate is too slow), the excess LN2 (rather than the gaseous nitrogen) begins to blow-by or exit through the exhaust system to the surrounding environment or the outside air. If the exhaust system is not being monitored, the LN2 source can remain on for an extended period and a significant amount of LN2 can be expelled to the outside air. Monitoring the output of the exhaust is problematic, because these vents are typically located outside the buildings involved, and the vented LN2 can thus be difficult to see or hear. Consequently, a significant amount of LN2 can be released and wasted due to blow-by, which also creates a substantial safety risk. Therefore, a pressing need exists for a system and method that can prevent blow-by of liquefied gases. As described in detail below, the present invention provides such a system and method, which resolves the above-described blow-by problems and other similar problems.

SUMMARY OF THE INVENTION

The present invention provides a system and method for preventing blow-by of liquefied gases, which senses the occurrence of blow-by and shuts off the source of the liquefied gas. In accordance with a preferred embodiment of the present invention, a system for preventing blow-by of LN2 is provided, which includes a temperature sensor located near an exhaust line of a heat exchanger, a shutoff valve located in an inlet line, and a controller coupled to the temperature sensor and the shutoff valve. The sensor measures the temperature of the exhaust, and provides a signal to the controller that indicates if the temperature of the exhaust approaches the temperature of LN2 . If the exhaust temperature approaches the temperature of LN2 , the controller sends a signal to the shutoff valve, which causes the valve to close and stops the flow of LN2 to the heat exchanger involved. The controller can also send an alarm signal to a display, which indicates to a user that the blow-by is occurring. If the exhaust temperature increases significantly above the temperature of LN2 (e.g., blow-by is no longer occurring), the controller can send a second signal to the shutoff valve, which causes the valve to open and resume the flow of LN2 .

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

FIG. 1 depicts a pictorial representation of an example system for preventing blow-by of a liquefied gas, which can be used to implement a preferred embodiment of the present invention; and

FIG. 2 depicts a pictorial representation of an example system for preventing blow-by of a liquefied gas, which can be used to implement a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

With reference now to the figures, FIG. 1 depicts a pictorial representation of an example system 100 for preventing blow-by of a liquefied gas, which can be used to implement a preferred embodiment of the present invention. For this illustrative embodiment, LN2 is used as a coolant in an example heat transfer application. As such, system 100 includes a temperature sensor 102 connected to an input of a controller unit 104. For example, controller unit 104 can be implemented with a suitable digital or analog process controller, microcontroller, digital processor, etc. An output of controller unit 104 is connected to an input of a shutoff valve 106. The shutoff valve 106 is located in series between an inlet tube 108 and a heat exchanger 114, and the temperature sensor 102 is coupled to an exhaust tube 110 of the heat exchanger 114, so that temperature sensor 102 can sense the temperature of the exhaust tube 110 at that location. As an option, the controller unit 104 is also connected to an alarm/display unit 116. For illustrative purposes, a muffler 112 for noise suppression of the rapidly expanding gaseous nitrogen produced at the output of the heat exchange process is shown located in series between the outlet of exhaust tube 110 and heat exchanger 114. Notably, although the example embodiment shown in FIG. 1 is described herein as using LN2 as a coolant for a heat exchanger application, the present invention is not intended to be so limited and can include any suitable application or process in which blow-by of a liquefied gas (e.g., LN2 , liquid helium, liquid oxygen, etc.) can occur.

In operation, for this example embodiment, shutoff valve 106 is normally open, and the liquefied gas (LN2 in this case) is being pumped from a storage tank (not shown) into inlet tube 108 and heat exchanger 114. During a normal heat transfer operation, heat exchanger 114 produces gaseous nitrogen having an average temperature of about 20 degrees Celsius in exhaust tube 110. Temperature sensor 102 couples an appropriate signal to controller unit 104 that indicates the temperature of exhaust tube 110 and the gaseous nitrogen flowing within exhaust tube 110. If the input LN2 flow rate surpasses the rate of the heat transfer process in heat exchanger 114, blow-by begins to occur and LN2 starts to flow through exhaust tube 110. As the excess LN2 passes by temperature sensor 102, it senses the dramatic drop in temperature (e.g., approaching 77 Kelvin) and sends a suitable signal indicating that temperature drop to controller unit 104. If controller unit 104 receives a temperature reading from temperature sensor 102, which indicates (e.g., by a dramatic drop in temperature) that LN2 is flowing through exhaust tube 110, controller unit 104 sends a suitable “off” command signal to shutoff valve 106. In response, shutoff valve 106 closes and terminates the flow of LN2 into inlet tube 108 and heat exchanger 114 and thus prevents blow-by. As an option, controller unit 104 can also send a suitable “alarm” signal to alarm/display unit 116 for a user to see and/or hear. Also as an option, if controller unit 104 subsequently receives a temperature reading from temperature sensor 102, which indicates (e.g., by a substantial increase in temperature) that LN2 is no longer flowing through exhaust tube 110, controller unit 104 can send a suitable “on” command signal to shutoff valve 106, which in response, reopens and allows LN2 to flow into inlet tube 108 and heat exchanger 114.

FIG. 2 depicts a pictorial representation of an example system 200 for preventing blow-by of a liquefied gas, which can be used to implement a second embodiment of the present invention. For this illustrative embodiment, a Dewar 206 (or similar containment vessel for liquefied gas) is being filled with LN2 . As such, system 200 includes a temperature sensor 210 connected to an input of a controller unit 212. For this example embodiment, controller unit 212 can be implemented with a suitable digital or analog process controller, microcontroller, digital processor, etc. An output of controller unit 212 is connected to an input of a shutoff valve 204. The shutoff valve 204 is located in series between an inlet tube 202 and Dewar 206, and the temperature sensor 210 is coupled to a vent tube 208 of Dewar 206, so that temperature sensor 210 can sense the temperature of the vent tube 208. As an option, the controller unit 212 is also connected to an alarm/display unit 214. Again, although the example embodiment shown in FIG. 2 is described herein as filling a Dewar with LN2 , the present invention is not intended to be so limited and can include any suitable application or process in which blow-by of a liquefied gas (e.g., LN2 , liquid helium, liquid oxygen, etc.) can occur during the filling of a containment vessel.

In operation, for this example embodiment, shutoff valve 204 is normally open, and the liquefied gas (LN2 in this case) is being pumped from a storage tank (not shown) into inlet tube 202 and Dewar 206. As long as Dewar 206 is not being overfilled, gaseous nitrogen having an average temperature of about 20 degrees Celsius is vented through vent tube 208. Temperature sensor 210 couples an appropriate signal to controller unit 212 that indicates the temperature of vent tube 208 and the gaseous nitrogen escaping out of vent tube 208. However, if the Dewar 206 is overfilled, blow-by begins to occur and LN2 starts to flow through vent tube 208. As the excess LN2 passes by temperature sensor 210, it senses the dramatic drop in temperature (e.g., approaching 77 Kelvin) and sends a suitable signal indicating that temperature drop to controller unit 212. If controller unit 212 receives a temperature reading from temperature sensor 210, which indicates (e.g., by a dramatic drop in temperature) that LN2 is flowing through vent tube 208, controller unit 212 sends a suitable “off” command signal to shutoff valve 204. In response, shutoff valve 204 closes and terminates the flow of LN2 into inlet tube 202 and Dewar 206 and thus prevents blow-by. As an option, controller unit 212 can also send a suitable “alarm” signal to alarm/display unit 214 for a user to see and/or hear.

It is important to note that while the present invention has been described in the context of a fully functioning system for preventing blow-by of a liquefied gas, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media, such as a floppy disk, a hard disk drive, a RAM, CD-ROMs, DVD-ROMs, and transmission-type media, such as digital and analog communications links, wired or wireless communications links using transmission forms, such as, for example, radio frequency and light wave transmissions. The computer readable media may take the form of coded formats that are decoded for actual use in a particular system for preventing blow-by of a liquefied gas.

The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. These embodiments were chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 

1. A system for preventing blow-by of a liquefied gas, comprising: a containment vessel including an inlet and an outlet, said containment vessel adapted to contain a quantity of a liquefied gas; a valve coupled between said containment vessel and a portion of said inlet, said valve adapted to block a flow of said liquefied gas into said containment vessel during at least one mode of operation; a sensor coupled to a portion of said outlet, said sensor adapted to output a signal associated with a current temperature of said portion of said outlet; and a controller unit coupled to said valve and said sensor, said controller unit adapted to send a control signal to said valve if said current temperature is less than or equal to a predetermined temperature, said control signal associated with said at least one mode of operation.
 2. The system of claim 1, wherein said containment vessel comprises a heat exchanger.
 3. The system of claim 1, wherein said containment vessel comprises a Dewar.
 4. The system of claim 1, wherein said liquefied gas is LN2 .
 5. The system of claim 1, wherein said liquefied gas is at least one of liquefied helium and liquefied oxygen.
 6. The system of claim 1, wherein said predetermined temperature is associated with a boiling temperature of said liquefied gas.
 7. The system of claim 1, wherein said predetermined temperature is substantially 77 Kelvin.
 8. The system of claim 1, wherein said predetermined temperature is associated with a substantial decrease of said current temperature during a predetermined period of time.
 9. The system of claim 1, wherein said outlet comprises an exhaust for a heat exchanger.
 10. The system of claim 1, wherein said outlet comprises a vent.
 11. A system for preventing blow-by of a liquefied gas, comprising: means for containing a quantity of a liquefied gas; means for blocking a flow of said liquefied gas into said means for containing; means for releasing said liquefied gas from said means for containing; means for generating a signal associated with a current temperature of said means for releasing; and means for receiving said signal and sending a control signal to said means for blocking, if said current temperature is less than or equal to a predetermined temperature.
 12. The system of claim 11, wherein said means for containing comprises a heat exchanger.
 13. The system of claim 11, wherein said means for containing comprises a Dewar.
 14. A method for preventing blow-by of a liquefied gas, comprising the steps of: enabling a liquefied gas to enter a containment vessel; enabling a gaseous form of said liquefied gas to exit said containment vessel; sensing a current temperature of said gaseous form of said liquefied gas; and blocking said liquefied gas from entering said containment vessel, if said sensed current temperature is less than or equal to a predetermined temperature.
 15. The method of claim 14, wherein the blocking step is performed with a shutoff valve.
 16. The method of claim 14, wherein the containment vessel comprises a heat exchanger.
 17. The method of claim 14, wherein the containment vessel comprises a Dewar.
 18. The method of claim 14, further comprising the step of: unblocking said liquefied gas from entering said containment vessel, if said sensed current temperature is substantially higher than said predetermined temperature.
 19. A computer program product, comprising: a computer-usable medium having computer-readable code embodied therein for configuring a computer processor, the computer program product comprising: a first executable computer-readable code configured to cause a computer processor to enable a liquefied gas to enter a containment vessel; a second executable computer-readable code configured to cause a computer processor to enable a gaseous form of said liquefied gas to exit said containment vessel; a third executable computer-readable code configured to cause a computer processor to sense a current temperature of said gaseous form of said liquefied gas; and a fourth executable computer-readable code configured to cause a computer processor to block said liquefied gas from entering said containment vessel, if said sensed current temperature is less than or equal to a predetermined temperature.
 20. The computer program product of claim 19, further comprising: a fifth executable computer-readable code configured to cause a computer processor to unblock said liquefied gas from entering said containment vessel, if said sensed current temperature is substantially higher than said predetermined temperature. 